This section provides information about those satellite sensors likely to be of greatest use for studying the human dimensions of global environmental change. Each of these sensors enables direct observation of the global land surface in a consistent fashion, with data having unique characteristics of spectral, spatial, and temporal resolution. To varying degrees, the data gathered by each sensor are suited for the variety of specific interests associated with monitoring the effects of natural events and human actions on land cover. Such interests may alternatively require high frequency of coverage, specific combinations of spectral information, or high spatial resolution. In many cases, the data of two or more sensors offer complementary characteristics, making joint use of data advantageous. (Joint use refers to the computerized merging or fusion of different data types into a single product, as well as to the synergistic use and analysis of different data types in the course of research.)
Several of the sensors included in this section either have or are expected to provide data over a period of many years (into the late 1990s and beyond 2000). These data are readily available from data center archives. The sensors include the U.S.National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer sensor, the U.S. Landsat Multispectral Scanner (MSS) and Landsat Thematic Mapper (TM) sensors, the French Systeme Probatoire d'Observation de la Terra (SPOT) High Resolution Visible (HRV) Sensor, the Indian Remote Sensing Satellite, and a variety of declassified sensors. The Figure of Observation Characteristics compares the current characteristics and future improvements planned for these earth-observing multispectral satellite sensors relative to the nominal spectral properties of vegetation, soil, and water. Figure 1 illustrates varying level of detail for selected cases of spatial resolution processed from these sensors. Lillesand and Kiefer (1987) provide greater detail on the satellite platforms and sensor operation in the chapter "Earth Resource Satellites" in Remote Sensing and Image Interpretation.
The recently deployed European Remote Sensing Satellite (ERS-1) and the Japanese Earth Resources Satellite (JERS-1) now provide Synthetic Aperture Radar Sensors image data for evaluating land cover, ocean, and ice surface characteristics. The Sea-viewing Wide Field of View Sensor slated for deployment in 1994, is expected to gather ocean color data. In the late 1990s, the Earth Observing System is anticipated to provide extensive global observations of the biosphere, atmosphere, and oceans.